This invention relates to the beneficiation of iron ore and, more particularly, to a process of beneficiating low-grade, siliceous oxidized iron ores by froth flotation.
Many low-grade iron ores are too low in iron and too high in silica-bearing gangue to be suitable for use in iron and steel making processes. Consequently, such ores must be treated to separate the iron oxide content from the gangue. Froth flotation processes have been employed for this purpose. In such processes the iron oxide is floated from the silica by use of anionic collectors, or a reverse flotation scheme is employed whereby silica is floated from the iron oxide by use of cationic collectors or anionic collectors activated by a calcium ion.
Many iron ores must be ground to a very fine size to permit liberation of iron oxides from the gangue, resulting in the reduction of some of the silica and other materials to slimes which interfere with the flotation process. This problem can be minimized by desliming the iron ore pulp before flotation. However, such a desliming step adds to processing costs and loss of the iron values. For example, losses up to as much as 25 to 30% of the iron are quite common in flotation processes including a desliming step.
While eliminating grinding of the ore to a degree at which slimes are artificially produced would alleviate problems associated with the presence of slime, such an approach cannot be used for many ores in which the iron oxide is tightly interlocked with silica and/or other gangue materials and fine grinding is required to obtain an acceptable liberation of the iron oxide. Processes have been proposed wherein flotation is effected in the presence of slime; however, none have been commercially adopted to any appreciable extent because the concentrate is of poor quality, the process is effective for a limited number of ores, precise control of the operating conditions is required and/or the number of process steps involved, the type and quantity of reagents used, etc., result in excessive operating costs.
Examples of prior art flotation processes employing anionic type collectors for floating iron oxide from a silica-bearing gangue are disclosed in U.S. Pat. Nos. 2,769,541 (Perry), 2,861,687 (Lord) and 3,589,622 (Weston). Examples of prior art flotation processes in which the silica-bearing gangue is floated from iron oxide are disclosed in U.S. Pat. Nos. 2,423,022 (Herkenhoff) and 3,292,780 (Frommer et al).